Funding for Victoria Police roadside operations has been frozen following revelations officers faked more than a quarter of a million breath tests.
The force found 258,463 tests were falsified since 2012, according to an audit by the force's Professional Standards Command and statisticians.
The figure represents 1.5 per cent of more than 17.7 million roadside tests over a five-year period.
Former Victorian police chief commissioner Neil Comrie will lead an investigation into why officers faked the tests by either placing a finger over the straw entry hole or by blowing into the straw themselves.
"Let me be clear, this is not an isolated occurrence, this is widespread behaviour," Professional Standards Command Assistant Commissioner Russell Barrett said on Thursday.
"Victoria Police is incredibly disappointed. It is incredibly poor behaviour by our members."
One theory was officers were trying to make themselves look more productive, he said, while the police union blamed unrealistic workloads.
While the main culprits behind the falsified tests are general duties and highway patrol officers, Mr Barrett could not say how many were involved.
No individual officers have been pinpointed and the practice was not found at supervised drug and alcohol bus test sites.
Some rural areas were also over-represented in the falsified results but the force would not reveal which ones.
While Mr Barrett admitted the behaviour amounted to misconduct, he said it did not involve any criminality or fraud.
"Our reputation is tarnished in the eyes of the TAC and the Victorian community. We can't walk away from that," he said.
"At the moment, TAC's funding has been suspended to Victoria Police."
The TAC makes about $12 million available to Victoria Police over a three-year period for what's known as an enhanced enforcement program.
The force needs to apply to use that funding and recent applications have been suspended until the commission is confident the issue has been resolved.
The suspension will not affect current random breath tests.
Police Association Victoria secretary Wayne Gatt blames the scandal on the unrealistic number of breath tests officers are expected to do.
Police Minister Lisa Neville says police "well and truly" exceed their roadside testing targets, adding officers will have done about 4.5 million this year.
"There's not this sort of pressure to meet some target. They're well above it so I think that's why there is a question here about why this has occurred," she said.
Independent Broad-based Anti-corruption Commissioner Robert Redlich said a complaint about the tests was made to Victoria Police last September and IBAC was notified of early data analysis results in February.
He said it was concerning that police didn't report the conduct internally or to IBAC, saying they have a "clear obligation not to turn a blind eye to any police misconduct".